A. Field of the Invention
The device of the present invention generally relates to molded case circuit breakers and, more particularly, to calibration adjusting means for a thermally actuated bimetal for molded case circuit breakers.
B. Description of the Prior Art
Circuit breakers and, more particularly molded case circuit breakers are old and well known in the prior art. Examples of such devices are disclosed in U.S. Pat. Nos. 2,186,251; 2,492,009; 3,239,638; 3,525,959; 3,590,325; 3,614,685; 3,775,713; 3,783,423; 3,805,199; 3,815,059; 3,863,042; 3,959,695; 4,077,025; 4,166,205; 4,258,403; and 4,295,025. In general, prior art molded case circuit breakers have been provided with movable contact arrangements and operating mechanisms designed to provide protection for an electrical circuit or system against electrical faults, specifically, electrical overload conditions, low level short circuit or fault current conditions, and, in some cases, high level short circuit or fault current conditions. Prior art devices have utilized an operating mechanism having a trip mechanism for controlling the movement of an over-center toggle mechanism to separate a pair of electrical contacts upon an overload condition or upon a short circuit or fault current condition. Such trip mechanisms typically have an armature movable in response to the flow of short circuit or fault current to rotate a trip bar of the trip mechanism to cause the pair of contacts to separate. Such trip mechanisms have also included a thermally actuated bimetal movable in response to an overload condition to separate the circuit breaker contacts. Many prior art devices have included a bimetal that has an operating portion spaced a predetermined distance from the trip bar and a set screw engaging the operating portion of the bimetal to adjust the spacing between the operating portion and the trip bar. In such prior art devices, stress may be applied to the operating portion of the bimetal by the pressure or friction between the calibration tool and the set screw. Such stress may affect the adjustment of the spacing between the operating portion of the bimetal and the trip bar. Additionally, in such devices any stress relieving in the bimetal due to heating will change the adjustment or calibration.
A need exists for dimensionally small molded case circuit breakers capable of fast, effective and reliable operation and, more specifically, for an accurate calibration adjusting means for the bimetal.